J. H. A. Whealler—Boulders of Cambridge Gravels. 201 
Rhomb-porphyry (2). 
(?)Nordmarkite. 
Pink granulitic granite, two large specimens. 
Orthophyre of North Berwick type. 
(?)Analcime-dolerite (Teschenite) of Forth Valley type. 
Cheviot porphyrite and lava. 
Coarse white granite. 
Large concretion with Serpula tetragona. 
A species of Gryphea, intermediate between arcuata and dilatata. 
To proceed to a detailed description of the new types recorded. 
The specimens may be classified according to their’ reputed source 
of origin, which sources may be conveniently divided as follows :— 
Scandinavia. 
Scotland and Scottish borders. 
Lake District. 
North-Eastern and Eastern England. 
Source unknown. 
ee Se 
Of necessity the majority of specimens are allocated to the last 
class. 
To deal with the divisions severally, commencing with an 
Scandinavian types. The only specimens which had been recorded 
at the time of publication of Rastall and Romanes’ paper, were 
thomb porphyry and a doubtful nordmarkite, or, rather, I should 
say, these were the only certain types. Since that time several 
more specimens of rhomb porphyry have been collected, notably 
by Professor Marr, one of which is remarkably large, measuring 
12 by 11 by 7 inches. This rock, however, is far from common at 
the Travellers’ Rest Pit, though it is found in greater abundance 
elsewhere in the Cambridge district. Laurvikite, which has been 
recorded from the district before, has been cellected at the pit, once 
only I believe, and that specimen a small and badly weathered one. 
One small specimen of the pink soda granite of Christiania has been 
collected. 
Perhaps the most important discovery from the pit, however, 
is a small boulder with a violet-brown groundmass, in which are 
scattered grains of quartz, small orthoclase felspars, and greenish 
plagioclase. This corresponds therefore very closely with the 
Sarna porphyry, according to Milthers? description of that rock. 
A second specimen has recently been collected bearing a strong 
resemblance to the last, but with a smaller amount of quartz and 
without plagioclase, so far as can be seen by the naked eye. The 
groundmass also is dark grey, rather than violet-brown. This 
strongly resembles the specimens of the Elfdal porphyry in the 
Natural History Museum. These rocks therefore belong to the Dala 
group of porphyries, as described by Milthers, a type not hitherto 
recognized in this neighbourhood. On looking through the collection 
1 Milthers, Indicator Boulders, D.G.U. II, R. Nr: 23, Copenhagen, 1909 ; 
and Geschiebe aus der Umgegend von Kénigsberg in Ostpreussen, Phys. ok. 
Gesell. zu Kénigsberg, 1888. 
